Extreme Weather’s Link to Climate Change Is Becoming Clearer

A
A s the effects of climate change become increasingly apparent, improvements in data collection and technology are enabling scientists to be more forward-leaning about the impact it has had on extreme weather.

Previously, climate researchers were generally very hesitant to discuss the influence of climate change in connection to a particular weather event. The standard explanation was that a warming world couldn’t be blamed for a specific storm or heat wave, though the likelihood of either instance increases with every notch on the thermometer.

But this is changing now that researchers have more information and more experience studying it.

“The science is advancing fast, and that may surprise a lot of people,” Jeff Rosenfeld, editor-in-chief of the Bulletin of the American Meteorological Society, told Seeker.

The Bulletin just published its latest look at the issue, with 17 studies examining the fingerprints of climate change on extreme events worldwide in 2017. They range from a drought that wilted crops and fueled wildfires across the northern Great Plains to dense cloud cover over Japan, from African droughts to flooding in Peru and Uruguay.

“The increase in odds has been so great, you could almost say this would not happen without climate change.”

Scientists can’t yet say that a specific storm or event was the direct result of climate change. They still couch their conclusions in the language of risk and odds. Or they say that climate change made a particular disaster worse, such as the flooding that followed Hurricane Florence in October or the sudden rainstorm that devastated Baton Rouge, La., in 2016.

But they’re now ingesting streams of data from land, sea, and satellite instruments, and are equipped with advanced processors and more sophisticated computer models with which to analyze it all. And they’re learning more about how to assess this impact and frame their findings, Rosenfeld noted.

These bleaching corals in Indonesia show how corals begin to bleach as warmer than normal water temperatures stress the symbiosis between coral and zooxanthellae. When zooxanthellae leave the coral, the coral turns pale. |
Getty Images

“When you go to the doctor and the doctor sees a pack of cigarettes in your pocket, he or she isn’t going to say, ‘You’re going to die of lung cancer,’ ” he said. “But the doctor can say, ‘I see you’re smoking cigarettes. I can tell you that’s going to raise the odds of lung cancer, and I can tell you how much it’s going to raise the odds of lung cancer.’ ”

It’s easier to find the fingerprint of climate change in some events, such as the oceanic heat waves that have damaged fisheries and coral reefs worldwide in recent years.

“The increase in odds has been so great, you could almost say this would not happen without climate change,” Richard Black, director of the London-based Energy and Climate Intelligence Unit, told Seeker.

But in the past year, researchers have published the results of 43 studies looking into the weather-climate connection and found evidence of that link in 32 of them, Black’s nonprofit research firm reports. And they’re able to produce those conclusions faster, sometimes while a longer-running event like a heat wave or a drought is still going on.

“I think that makes a massive difference in terms of public awareness,” Black said. “You’re getting the analysis out there while the event is still very fresh in the public memory.”

When the National Oceanic and Atmospheric Administration (NOAA) just put out its annual Arctic Report Card, it found that temperatures in the far North are going up at twice the average rate of the rest of the world. This was, the report said, “driving broad change in the environmental system in predicted and, also, unexpected ways.”

The effect that warming appears to be having on weather in the rest of the Northern Hemisphere is also under close scrutiny. Much of that weather is driven by the jet stream, an atmospheric current driven by the temperature difference between the Arctic and the warm air of the lower latitudes. When the temperature difference between those regions shrinks, the jet stream gets weaker — and a weaker current tends to meander. It flows in slow waves, bringing blasts of cold Arctic air southward behind it while drawing warm air northward.

This effect was seen in North American cities like Boston and New York, where shirtsleeve temperatures occurred in the middle of last winter, while Europe was plunged into a deep freeze that brought snow as far south as Rome.

Researchers are increasingly confident of that connection. But the details are still being worked out, and different effects may be seen in assorted locations and seasons, and with such variables as ocean temperature fluctuations.

“The uptick in extreme weather events — especially those related to persistent patterns — is certainly consistent with our expectations for the impacts of increasing Arctic amplification,” Jennifer Francis, an atmospheric scientist who wrote the NOAA report’s chapter on the subject, told Seeker. “But given the relatively short time period of actual observations since the Arctic started warming rapidly, the signal is still hard to tease out of all the noise.”

“We have learned a lot in recent years, but there’s still much we still don’t know because the climate system is so complicated and noisy,” she added.

That improved attribution is likely to have effects beyond your daily weather report. It could affect business decisions like banks or insurance companies, which often hold the fate of a big project in their hands.

“The world is built on understanding risks, pricing it for one another and passing it along to investors or insurers or health care providers or government,” Rosenfeld said. “All of these things depend on understanding very well what the risks are of extreme events, not just the day-to-day stuff.”

Global average temperatures now run about 1 degree Celsius (1.8 degrees Fahrenheit) warmer than the 1880s, when people started keeping widespread temperature records. Nearly all countries have agreed to try to rein in the carbon emissions that are fueling this warming enough to limit climate change to somewhere between 1.5 and 2 degrees C by the end of the century — the point beyond which scientists say warming will produce catastrophic change.

But emissions have started going up again after remaining relatively stable for three years running, adding to the potential for more extreme weather patterns to come.